The Old Testament or the Hebrew Scriptures constitutes the first major part of the Christian Bible, usually divided into the categories law, history, poetry and prophecy. All of those books were written before the birth of Jesus.
The Protestant Old Testament consists of the same books as the Tanakh, but the order and numbering of the books are different. The exact number of books depends on whether certain disputed books are included, but all Christian groups agree on 39 books. (The Jewish tradition counts them as 24 books, with Samuel, Kings, and Chronicles forming one book each, the 12 minor prophets grouped into one book, and Ezra and Nehemiah combined into one.) The Roman Catholic and Eastern Orthodox include an additional seven books, called the Deuterocanonical books, which Protestants exclude as apocryphal.
The Old Testament text used by the earliest Greek-speaking, Christians was the Septuagint, a Greek translation that was widely held by Jews in the first century to be authoritative and which included the Deuterocanon.
The major difference between the Old Testament and the Jewish scripture, the Tanakh, is in the order of the books. The order of the books of the Old Testament is:
Jews themselves do not accept the New Testament or the characterization of the Tanakh as the Old Testament (although many Jews accept Jesus as a historical figure and even as a student of a Tannaitic Sage).
The relationship between the Old Testament and the New Testament is controversial among Christians. There is some debate among Protestant scholars over the issue of whether the New Testament applies to Jewish people, but there is very little debate over its applicability to Gentiles. Similarly, the degree to which the Old Testament and its laws applies to Christians. Very few Christians, for example, follow the dietary laws within the Old Testament, whereas almost all Christians believe that the Ten Commandments are applicable. The question of which Old Testament laws are applicable affects debates on homosexuality and the ordination of women in the priesthood.
Some historical groups such as Gnostics have gone so far as to assert that the God of the Old Testament is a different being that the God of the New Testament. Most Christian groups believe that this view is heresy.
Thus, some scholars prefer Hebrew Bible as a term that covers the commonality of the Tanakh and the Old Testament while avoiding sectarian bias.
The New Testament text however does contain many references to the Old Testament, especially in relation to the fulfillment of prophecies concerning the promised messiah, whom Christians believe to be Jesus. In Christian theological views this expectation, present fulfillment and eschatological fulfillment of the divine, eternal kingdom under the headship of Christ are the thread running through both Testaments.